Eur. Phys. J. E (2006) 20: 1-6
https://doi.org/10.1140/epje/i2005-10074-x

Regular Article

Spontaneous condensation in DNA-polystyrene- b-poly(l-lysine) polyelectrolyte block copolymer mixtures

¹ School of Chemistry, The University of Reading, P.O. Box 224, RG6 6AD, Whiteknights, Reading, UK
² Procter Department of Food Science, University of Leeds, LS2 9JT, Leeds, UK
³ Research Institute of Molecular & Cell Biology, Faculty of Biological Sciences, University of Leeds, LS2 9JT, Leeds, UK
⁴ Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128, Mainz, Germany
⁵ Institut des Matériaux, Laboratoire des Polymères, École Polytechnique Fédérale de Lausanne (EPFL), Bâtiment MX-D, CH-1015, Lausanne, Switzerland

^* e-mail: V.Castelletto@reading.ac.uk

Received: 14 October 2005
Accepted: 10 February 2006
Published online: 27 April 2006

Abstract

We investigated the condensation of calf thymus DNA by amphiphilic polystyrene_m-b-poly(l-lysine)_n block copolymers ( PS _m -b- PLys _n , m, n = degree of polymerization), using small-angle X-ray scattering, polarized optical microscopy and laser scanning confocal microscopy. Microscopy studies showed that the DNA condenses in the form of fibrillar precipitates, with an irregular structure, due to electrostatic interactions between PLys and DNA. This is not modified by the presence of hydrophobic PS block. Scattering experiments show that the structure of the polyplexes corresponds to a local order of DNA rods which becomes more compact upon increasing n. It can be concluded that for DNA/ PS _m -b- PLys _n polyplexes, the balance between the PLys block length and the excess charge in the system plays an essential role in the formation of a liquid crystalline phase.